As an X-ray analytical technique in a region of nano-meter order, known techniques are a SEM-EDX (STEM-EDX) or a SEM-WDX (STEM-WDX), for scanning an extremely fine electron probe on a sample and dispersing an X-ray generated from an irradiated local region with an electron beam. (EDX; Energy Dispersive X-ray Spectroscopy, WDX; Wavelength Dispersive X-ray Spectroscopy). The SEM-EDX (STEM-EDX) or the SEM-WDX (STEM-WDX) is a device in which an energy dispersive X-ray spectrometer (EDX) is installed in a SEM (STEM) or a wavelength dispersive X-ray spectroscopy is installed therein.
The WDX spectroscopy is a spectroscopy, which drives a diffraction grating as a dispersive crystal and uses a Bragg diffraction equation (2dsin θ=nλ). “d” represents the space of a lattice plane of the diffraction grating, “θ” represents an incidence angle at which an X-ray enter the lattice plane, “n” represents a diffraction order, and “λ” represents the wavelength of the X-ray. The WDX spectroscopy can perform an analysis with high sensitivity and with high accuracy, because overlapping of the X-ray spectrums can be eliminated, and because the energy resolution is higher (one or more than one digit larger) than an energy resolution 120 eV of the EDX spectroscopy, and the energy resolution is in a rang between several eV to tens of eV. That is, the energy resolution is larger than the energy resolution 120 eV of the EDX spectroscopy.
Generally, there are two types of WDX spectroscopy. As illustrated in FIG. 1, one type of WDX spectroscopy disperses and detects an X-ray, while rotating a planer shaped diffraction grating 16 with a multilayer film and driving an X-ray detector 18. To realize parallel entering of the X-ray toward the planer shaped diffraction grating 16, and to increase the yield of an X-ray 3 generated from the sample 15, an X-ray condensing lens 19 is provided between the sample 15 and the diffraction grating 16 (for example, Patent literature 1). To realize parallel entering of the X-ray 3 toward the diffraction grating 16, slits may sometimes be provided between the sample 15 and the diffraction grating 16.
As illustrated in FIG. 2, in the other type of spectroscopy, a curved-type (called as Johann or Johansson-type) diffraction grating 20 and the detector 18 are provided. In addition, the X-ray is dispersed and detected, while the curved-type diffraction grating 20 and the detector 18 are driven on a Rowland circle 21. In Patent literature 2, to have a compact X-ray detection system, an irregularly spaced diffraction grating is used for a dispersive crystal, and an X-ray is caused to obliquely enter the irregularly spaced diffraction grating. Then, a plurality of diffracted rays of light dispersed by the irregularly spaced diffraction grating are simultaneously detected by a CCD detector. To correspond to a high energy X-ray from a low energy one, a plurality of diffraction gratings are prepared, and there is provided a mechanical mechanism for exchanging and replacing/installing the diffraction grating, to select/install the diffraction gratings in accordance with X-ray energy of a target to be analyzed. As described above, the WDX device using the irregularly spaced diffraction grating and a position detector (CCD) acquires an X-ray spectrum as a reference of an energy position and an X-ray spectrum of a target to be evaluated. An energy value of the X-ray spectrum of the target to be evaluated is obtained based on a relative amount of X-ray spectrum energy position as a reference.